This invention relates to methods for preparing synthetic composition board. More particularly, this invention relates to a process for preparing wood composition board which involves applying a pigmented coating to the surface of a fibrous mat prior to subjecting the mat to a press treatment.
Several methods have been suggested for preparing synthetic fiberboards or hardboards which are based upon wood particle chips or other lignocellulose fibers. These products are generally prepared by forming a mat of the wood precursor and consolidating the mat into a board by the application of heat and pressure. One major problem in forming these products into a unitary mat has involved release of the densified wood composite from the hot press plates. Another major problem exists with wood composition products, in that extractives, such as wood tannin or sugars and synthetic waxes tend to migrate to the surface and form tacky spots on the exterior of the finished composition board. The tacky spots collect dirt and cause unsightly spotting.
U.S. Pat. No. 4,237,087 discloses a water-borne, base coat composition which facilitates the embossing of wood-based particle board. The coating composition contains an acrylic emulsion resin, a urea resin, and an acid catalyst. However, no disclosure is made of the use of platelet form talc.
U.S. Pat. No. 4,201,802 also discloses a composition for the surface sealing of hard board products. However, the coating composition employed in this patent is a polymer of polyvinyl alcohol employed in combination with a volatile amine, emulsified fatty acids or esters, and aluminum stearate. While the patent does disclose the use of talc as a general purpose inert pigment, it does not disclose the particular type of talc employed nor the benefits derived from its use.
Platey talc is a known pigment which is most often used in forming undercoatings for metals because it tends to improve sanding properties and water resistance. However, its use in pigmented prepress coatings has not been disclosed previously.
Accordingly, it is an object of this invention to prepare in-press pigmented coatings for composition board, which coatings exhibit a smooth, embossed or textured surface.
It is another object of this invention to prepare pigmented coatings which exhibit excellent press release properties.
It is still another object of this invention to prepare sealers which limit or eliminate the surface migration of wood tannin, sugars or low melting waxes with attendant discoloration, dirt attraction and spotting.
These and other objectives are obtained by employing the process of the instant invention.